1. Field of the Invention
The present invention relates to a surface inspection apparatus to inspect an inspection subject (such as a particle and a flaw) on the surface of a film-coated wafer or other film-coated inspection subjects.
2. Related Art
Conventionally, when inspecting the surface of a transmissive film, a metal film, or the like of the film-coated wafer, a luminous flux has been made incident with a low angle to detect a particle on the surface. However, in surface inspection of the film-coated wafer on which the transmissive film was formed, reflectivity has varied depending on a film thickness and a material of the transmissive film and it has not been possible to ensure detection sensitivity at a constant level when the film thickness was not uniform.
When the film thickness was fixed, a plane of polarization has been switched in P-polarized light, S-polarized light, circular polarized light, and PS-polarized light to find optimum polarization conditions, and thus the particle has been detected.
However, in recent years, a CMP (chemical mechanical polishing) process has been introduced in processing of the film-coated wafer with microfabrication thereof. Once the processing such as the CMP was introduced in the processing of the film-coated wafer, the thickness of a film formed on the film-coated wafer varied in each wafer and the thickness scarcely has become uniform always.
The film thickness varies for each wafer when the CMP is applied for the film-coated wafer on which the transmissive film has been formed. Due to the variation of reflectivity caused by the varied film thickness, it has become difficult to ensure detection sensitivity of a constant level in the surface inspection of the film-coated wafer after the CMP processing. There are cases where particle detection sensitivity drastically reduces in the surface inspection of the film-coated wafer on which the transmissive film has been formed depending on an inspection position.
However, the CMP processing is essential to the microfabrication technology.
In addition, there exists a demand for an apparatus that can detect the particle such as a flaw and a CMP residue with good sensitivity.
Moreover, wafers of a new structure that pursue low electric consumption and high-speed operation such as an SOI wafer, for example, have been available. These wafers have a structure of a plurality of films by a thin Si film, SiO2 film and an Si base, and there have been cases of causing interference to widely vary sensitivity due to the relationship with an incident wavelength depending on the inspection position of the wafer surface.
The object of the present invention is to provide a surface inspection apparatus to perform surface inspection for a film-coated wafer or other film-coated inspection subjects, that is, inspection for a particle, a flaw, or the like, with stable sensitivity.
The present invention is one that has improved a surface inspection apparatus to inspect an inspection subject (such as a particle and a flaw) on the surface of the film-coated wafer or the other film-coated inspection subjects.
In a typical example of the present invention, the surface inspection apparatus comprises: a light source section that emits a first luminous flux and a second luminous flux; an irradiation optical system that irradiates the first luminous flux and the second luminous flux on the surface of the film-coated inspection subject; a displacement section that relatively displaces the film-coated inspection subject and an irradiation luminous flux from the irradiation optical system; a light-receiving optical system that receives scattered light generated from the inspection subject on the film-coated inspection subject after irradiation of the first luminous flux from the irradiation optical system and scattered light generated from the inspection subject on the film-coated inspection subject after irradiation of the second luminous flux from the irradiation optical system; a first light-receiving section that transforms the scattered light of the first luminous flux received by the light-receiving optical system into a first light reception signal; a second light-receiving section that transforms the scattered light of the second luminous flux received by the light-receiving optical system into a second light reception signal; and a sensitivity stabilizing section that synthesizes the first light reception signal and the second light reception signal to form a signal for sampling.
Preferably, a first characteristic of the first luminous flux and a second characteristic of the second luminous flux are wavelengths or polarization component of the luminous fluxes. The sensitivity stabilizing section selects either one of the first light reception signal and the second light reception signal for every inspection position of the film-coated inspection subject surface, and synthesizes the first light reception signal and the second light reception signal. Further, the sensitivity stabilizing section selects a light reception signal from which a detection sensitivity closer to a desired detection sensitivity has been obtained out of the first light reception signal and the second light reception signal for every inspection position of the film-coated inspection subject surface, and synthesizes the first light reception signal and the second light reception signal. Furthermore, the sensitivity stabilizing section selects a light reception signal from which a higher sensitivity has been obtained out of the first light reception signal and the second light reception signal for every inspection position of the film-coated inspection subject surface, and synthesizes the first light reception signal and the second light reception signal.
Preferably, a combination of the first luminous flux and the second luminous flux is a combination of luminous fluxes such that either the first light reception signal or the second light reception signal is obtained with predetermined detection sensitivity for every inspection position of the film-coated inspection subject surface.